Such an arrangement is described, e.g., in DE 297 18 405 U1, DE 298 16 659 U1, and EP 0 658 866 B1. In these documents, methods are disclosed in which the measurement signal is transmitted in a first channel, and the message signal is transmitted in a second channel. The first channel comprises a coupling stage, and the second channel comprises a transmitter or another coupling stage. Thus, overall two DC-isolated channels are required. The use of two DC-isolated channels, however, is cost intensive and has high spatial requirements.
In a signal feed isolator for measurement signals (DE 103 22 262 A1), only one two-conductor channel is required for the transmission of the signals, in which a voltage converter is used for the DC isolation in the transmission path, but an auxiliary power supply circuit is needed to prepare the received voltage signals according to the actual power requirements. With this circuit, however, no transmit-and-receive systems are connected to active current outputs because the energy is made available by the supply circuit, and thus, two voltage sources would work against each other.
A circuit arrangement for potential-free signal transmission between two electronic units by means of a transformer is also known (DE 35 33 278 C2), in which the secondary winding of the transformer is short-circuited for the presence of a return message signal. However, the control signal and return message signal must be performed one after the other, i.e., the simultaneous transmission of a current signal from one unit and a voltage signal from the other unit is not possible by means of a single two-conductor channel.